The invention relates to a blow molding machine and method for blow molding and sealing aseptic bottles, which, subsequent to molding, are opened and filled without the necessity of sterilization before filling.
In order to blow mold sterile bottles it is necessary to sterilize all tooling which contacts and may contaminate the interior of the parison or bottle. It is difficult to maintain the sterility of a blow pin used in shuttle blow molding because of the large size and blunt shape of the pin and the necessity of extending the pin a relatively long distance into the neck recess of a closed blow mold.
During blow molding of aseptic bottles sealed closed in the molds, it is necessary to first blow the bottle and then to reduce the interior pressure to below atmospheric pressure prior to sealing the bottle. This is because the blown bottles contain hot plastic which gives off residual heat during cooling. This heat warms the gas in the sealed bottle to increase the pressure in the sealed bottle.
The plastic in the bottle stabilizes in a permanent shape long after the bottle is removed from the mold. When the bottle is sealed closed at atmospheric pressure the gas in the bottle is warmed and increases the pressure in the bottle above atmospheric pressure to bow the walls of the bottle outwardly prior to stabilization of the plastic. The plastic bottle then stabilizes with undesired bowed walls or bottom. Reducing the interior pressure of a sealed aseptic plastic bottle blown using a blow needle is explained in U.S. Pat. No. 5,037,684, the disclosure of which is incorporated herein by reference in its entirety.
The pressure of the air in the aseptic bottle must be reduced below atmospheric pressure before the bottle is sealed. Blow air is conventionally withdrawn through the same passage used to flow blow air into the bottle. Exhaustion of blow air from the bottle through a common blow exhaust passage incurs the risk that rupture of the parison or bottle will result in drawing of nonsterile atmospheric air through the blow passage while removing blow air and will contaminate the passage. When the blow passage is contaminated subsequently blown bottles may be contaminated. The blow molding machine must be shut down and resterilized before manufacture of aseptic bottles can recommence. This is a lengthy and time-consuming process.
Accordingly, there is a need for an improved shuttle blow molding machine and method for blow molding sealed aseptic plastic bottles, which maintains the sterility of the blow pin and the blow passage during operation of the machine. Additionally, the machine should assure that rupture of a parison or bottle does not result in atmospheric air being withdrawn through the blow tube, which requires resterilization of the machine.
The invention is a blow molding machine with an improved blow pin assembly and method for shuttle blow molding to blow and seal aseptic bottles having a desired shape and which, when opened, are sterile and ready for filling. The machine maintains the sterility of the blow pin by surrounding the pin with sterile air and flowing the sterile air along the length of the pin in a laminar, circumferential flow extending around the blunt end of the pin. The laminar flow of sterile air adheres to the sides of the pin and, due to the Coanda effect, flows around the end of the pin to completely surround the end of the pin with sterile air and shield the pin from contaminated air.
After molding, the blow pin is retracted into a sterile chamber in a blow pin housing. The housing is connected to the pin by two narrow and easily flexed rolling diaphragm seals. The rolling diaphragm seals provide redundant protection against contamination of the blow pin chamber from unsterilized atmospheric air. A low-pressure chamber between the two seals increases the useful life of the seals and maintains sterility of the sterile chamber in the unlikely event the seals leak. The differential pressure across each seal assures that during blow pin extension and retraction the seals properly contact the adjacent surfaces of the housing and pin and do not wrinkle.
During blowing, high pressure blow air is flowed through a blow passage in the pin and into a parison held in a closed mold cavity. The air expands the molten parison to blow the bottle. After blowing, the blow air is exhausted from the blow cavity through an exhaust passage separate from the blow passage. The pressure in the blown bottle is reduced below atmospheric pressure prior to sealing the bottle closed. In this way, the bottle will assume the proper shape when the plastic in the bottle is fully stabilized. The provision of a separate exhaust passage for withdrawing blow air from the interior of the bottle assures that no exhaust air flows through the blow passage. This is important in the event a parison or bottle accidentally ruptures or is not properly captured by the mold, permitting flow of atmospheric air into the bottle or parison and out through the blow pin. Atmospheric air withdrawn through the exhaust passage may contain contaminants, which would destroy the sterility of this passage. However, such contamination would not destroy the sterility of the blow passage and would not prevent the machine from blowing sealed aseptic bottles. After the ruptured parison or bottle is ejected, the machine continues to blow sealing aseptic bottles as before, without the need for resterilization.
Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention, of which there are four sheets and one embodiment.